1. Field of the Invention
The present invention relates to a display device used in a large-screen luminescent display, and particularly to a display device capable of preventing adverse effect caused by electromagnetic noise from a driving circuit generated by on/off of light emitting elements.
2. Description of the Related Art
For example, a full-color large-screen luminescent display typically has a plurality of display units arranged next to each other, each display unit contains a plurality of pixels, where a combination of Red (R), green (G), and blue (B) light emitting diodes is defined as a pixel. Such a display unit is constructed as a combination of a display portion made up of light emitting diodes and a driving circuit for controlling the lighting of each light emitting diode. In the display portion, pixels, each of which is made up of a combination of the light emitting diodes which emit RGB lights respectively, are arranged in matrix, and the lead electrodes of the light emitting diodes are exposed from the back side of the circuit board. Circuit components such as IC, transistor, and a power connector are mounted on the circuit board having the driving circuit to control lighting of the light emitting diodes. A wiring pattern connected to the power connector is formed on the circuit board.
There have been known various measures for reducing adverse effect of electromagnetic noise originated in the circuit components due to on/off operations of the light emitting diodes and that originated in the entire wiring pattern connected to the power connector. In one example, a shielding member for preventing transmission of the electromagnetic noise is disposed to reduce the adverse effect of the electromagnetic noise.
For example, as described in JP 2007-177154A and JP 2001-242795A, as a measure to reduce adverse effect of electromagnetic noise, a shielding member is disposed between a frame and a frame mounting surface of the case, a screw is inserted into the through hole defined in the frame and is further placed into a screw receiving portion provided in the case to fix.
In this instance, the screw receiving portion is typically made of a metal material to secure sufficient fixing strength. The shielding member is electrically connected to the screw receiving portion, and is further connected to a grounding link provided to the case.
However, when the screw is placed into the screw receiving portion made of a metal material or the screw is taken out from the screw receiving portion, friction between the surfaces of the screw receiving portion and the screw may cause the surface of the metal to wear, resulting in deformation of the screw. Then, the screw becomes unable to fit tightly in the screw receiving portion and it raises concern about the fixing strength. For this reason, repeated screwing and unscrewing operations cannot be performed actively and it becomes difficult to replace the frame frequently.
To avoid such a problem, a screw having a structure capable of sustaining repeated screwing and unscrewing operations has also been proposed to use. For example, repeated screwing and unscrewing operations are possible with a so called metric screw thread. However, a metric screw thread has a structure to prevent loosening of a screw, and the loosening preventing structure results in high screw head. As described above, when the height of the screw head is increased, light from the light emitting elements may be blocked by the screw head which may cause reduction in display quality of the display device. Meanwhile, a screw which is designed specifically for a resin (for example, a tapping screw) and which is capable of sustaining repeated screwing and unscrewing operations with respect to a member made of resin material, is commonly used. If the material of the screw receiving portion is made of a resin to allow such a tapping screw to be threaded therein, an electric connection between the screw receiving portion and the shielding member cannot be established because a resin is an insulating material. Therefore, instead of establishing an electric connection with a shielding member at the screw receiving portion, there raises a need to separately provide an electrical connection part between the shielding member and the grounding link of the case.
Therefore, an object of the present invention is to provide a display device which includes together with a frame, a shielding member is fixed to a case through a screw, the device is capable of sustaining repeated screwing and unscrewing operation while maintaining an electric connection between the shielding member and a screw receiving portion for the screw to be screwed in.